Once you speak with Darion you will be asked if you are ready to fulfill the task. When you are ready you will be zoned into an instance in which you are charged with killing Grand Inquisitor Te'Lex.

Upon zoning in you will be faced with Acolyte Lin'Val. After killing the Acolyte you will be faced with the Grand Inquisitor himself.

The Grand inquisitor is actually a ring event. Every kill on the Inquisitor will raise a recently killed magus into a slightly harder version of the Inquisitor. Each resurrected Inquisitor will automatically agro about 15 seconds after killing his previous incarnation. Note that these only scale up to lvl 70. Anyone 75+ will find this super easy.